Distinct colony boundaries and larval discrimination in polygyne red imported fire ants (Solenopsis invicta)

Abstract

Evaluating the factors that promote invasive ant abundance is critical to assess their ecological impact and inform their management. Many invasive ant species show reduced nestmate recognition and an absence of boundaries between unrelated nests, which allow populations to achieve greater densities due to reduced intraspecific competition. We examined nestmate discrimination and colony boundaries in introduced populations of the red imported fire ant (Solenopsis invicta; hereafter, fire ant). Fire ants occur in two social forms: monogyne (colonies with a single egg-laying queen) and polygyne (colonies with multiple egg-laying queens). In contrast with monogyne nests, polygyne nests are thought to be interconnected due to the reduced antagonism between non-nestmate polygyne workers, perhaps because polygyne workers habituate the colony to an odor unique to Gp-9-carrying adults. However, colony boundaries and nestmate discrimination are poorly documented, particularly for worker-brood interactions. To delimit boundaries between field colonies, we correlated the exchange of a N-glycine tracer dissolved in a sucrose solution with social form. We also evaluated nestmate discrimination between polygyne workers and larvae in the laboratory. Counter to our expectations, polygyne colonies behaved identically to monogyne colonies, suggesting both social forms maintain strict colony boundaries. Polygyne workers also preferentially fed larval nestmates and may have selectively cannibalized non-nestmates. The levels of relatedness among workers in polygyne colonies was higher than those previously reported in North America (mean ±SE: 0.269 ± 0.037). Our study highlights the importance of combining genetic analyses with direct quantification of resource exchange to better understand the factors influencing ant invasions.

Assessing colony elimination in multicolonial ants: Estimating field efficacy of insecticidal baits against the invasive dark rover ant (Brachymyrmex patagonicus)

“…Due to the unicolonial structure observed in most treated species, using microsatellite markers to test for colony elimination has not been readily applied in ants as it would not provide useful information regarding the fate of colonies. Yet, like B. patagonicus , several pest ant species are not supercolonial, and exhibit multicolonial populations 63–66 . For these species, the assessment of colony density could therefore be useful in determining the overall success of a treatment 67 .…”

Non‐native stinging ant interactions with native anurans

“…Whereas there are sympatric native ants that also deliver venomous stings (e.g., Myrmica and Solenopsis spp. ), they do not occur in the densities nor form the overwhelming supercolonies of the invasive ants (Goodman & Warren II, 2019; Kjeldgaard et al, 2022; Warren II, Reed, et al, 2019).…”